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Covalent compounds form when nonmetallic atoms share electrons to become more stable. There are two types of covalent bonds: polar and non-polar. Covalent compounds have low melting and boiling points, are flammable, and do not dissolve or conduct electricity in water.
Covalent compounds are substances that form when two or more different elements are joined by a covalent bond. A covalent bond forms when two nonmetallic atoms share an electron. Atoms bond together in an attempt to become more stable. In general, atoms are most stable when they have the same amount of electrons as the nearest noble gas, and this usually means having eight electrons in their outer shell. In ionic bonds, this is accomplished by an atom with stronger electronegativity – the amount of attraction an atom has on electrons – stealing electrons from those with lower electronegativity. For covalent compounds no atom is strong enough to steal electrons and then share them.
There are two types of covalent bonds that can form covalent compounds: polar bonds and non-polar bonds. Polar bonds usually consist of several atoms unequally sharing electrons. This is often the result of a stronger electronegative atom bringing electrons closer together than a weaker atom. Since the electron spends most of its time closer to one atom than the other, the result is a covalent compound that has a partially negative end and a partially positive end.
Nonpolar covalent bonds are usually formed by two atoms sharing electrons equally. With these types of bonds, electrons spend the same amount of time with each atom, so there are no polar ends. A great example of a polar molecule is water which has the chemical formula H2O. In this case, the oxygen atom attracts electrons more to itself than the two hydrogen atoms, resulting in a covalent compound that is partially negative at the oxygen end and partially positive at the hydrogen end. An example of a non-polar molecule is the methane molecule (CH4) in which all atoms share their electrons equally.
In general, covalent compounds have a low melting point and boiling point compared to ionic compounds. Also, a substance composed of covalent compounds tends not to be as hard as one composed of ionic compounds. These characteristics are the result of the ease with which the molecules are able to separate. Although the atoms that make up the molecules in a covalent compound are tightly bonded, the individual molecules that make up the substance may have little hold on each other. For example, a person may have difficulty separating the hydrogen and oxygen in a water molecule, but boiling water, separating the molecules so that the water turns from liquid to gas, is a more difficult task. easy.
Other characteristics of most covalent compounds are their inability to dissolve and their inability to conduct electricity in water. Finally, covalent compounds tend to be flammable compared to ionic compounds. This flammability occurs because many covalent bonds tend to consist of carbon and hydrogen. Hydrogen and carbon can burn in the presence of heat and oxygen to form carbon dioxide and water in a reaction called combustion. As with all these properties, there are exceptions to the rule, for example, covalent bonds that do not have carbon or hydrogen in their composition do not tend to burn.
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